This invention relates to high speed, high power silicon controlled rectifiers, and more specifically relates to a novel silicon controlled rectifier and process for manufacture thereof which allows connection of a flat pressure contact to the upper surface of an emitter contact while preventing accidental contact to the surface of a gate contact which is interdigitated with the emitter contact.
High speed, high power controlled rectifiers in which contact is made to the emitter contact layer by a molybdenum expansion plate or the like are well known. Such devices are shown, for example, in U.S. Pat. No. 3,609,476.
In order to make the silicon controlled rectifier or thyristor operate at as high a speed as possible, it is preferable to interdigitate the gate and emitter contacts so that the device will turn on over its full area as rapidly as possible and thus be capable of operation with a high rate of rise of anode to cathode current. When the device is to have high current capacity and is made of a relatively large area wafer, it is also desired to make pressure contact to the device through the above-described expansion plate which has thermal coefficient expansion characteristics similar to those of silicon. The expansion plate is pressed into high pressure contact with the emitter contact. A gate lead is then connected to the gate area which is interdigitated with the emitter.
Copending application Ser. No. 196,684, noted above, discloses a novel method for building up the emitter contact layer to a level above that of the gate contact layer which is interdigitated therewith, which method lends itself to high production rates and inexpensive processing. Other processes are known for making interdigitated contacts which are flat but terminate in spaced, parallel planes. With this kind of structure, an expansion plate can make high pressure contact with the emitter contact surface. However, it has been found that the expansion plate can deflect enough or otherwise contact the gate contact surface, thus shorting the gate contact to the emitter contact.